JPH0467032B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a low temperature pumping device using a gas flow control valve, and particularly to a low temperature pumping device using a gas flow control valve that performs complete throttling. It is related to the device.

PRIOR ART Throttled cryogenic pumps are already known, as shown in US Pat. No. 4,285,710. In this patent, a pump is provided with a throttle valve located across the opening of the pump facing the process chamber. This throttle valve includes a fixed portion disposed to intersect the gas flow path and a sliding vane. A plurality of openings are formed in the fixed part, and the sliding vane closes the openings by sliding laterally. When the sliding vane closes the opening in the fixed part, the passage of gas is blocked.

[Problem to be Solved by the Invention] Although cryogenic pumps of the type described above have achieved commercial success, they suffer from the drawback that the capacity of the pump cannot be fully utilized. This is because the fixed portion of the throttle valve occupies a fairly large portion of the gas flow path even when the valve is fully open. Such problems are
It is not limited to the throttle valve shown in this patent. Virtually all throttle valves have a portion of the vane structure or a support that blocks the portion of the opening that provides access to the pump.

Therefore, an object of the present invention is to use a throttle valve that can reliably block gas flow in a fully closed state and minimize the number of members that act as a barrier to gas flow in a fully open state. An object of the present invention is to provide a cryogenic pumping device. Such a cryogenic pumping device would be more effective than conventional ones.

[Summary of the Invention] A cryogenic pumping device according to the present invention includes a cryogenic pump and a radial vane throttle valve. A cryogenic pump has a cooled outer wall for pumping a first stage of gas condensable at intermediate temperatures and a second stage pumping of gas condensable at low temperatures.
and a cooled inner wall for stage pumping. The cryogenic pump also has an opening facing the processing chamber to be pumped. A radial vane throttle valve is positioned across the aperture to throttle the aperture.

The radial vane throttle valve includes an annular flange having a continuous inner circumferential surface and a continuous outer circumferential surface spaced from the inner circumferential surface. The inner circumferential surface and the outer circumferential surface are connected to each other in a manner that blocks gas flow therebetween.

The throttle valve further includes a plurality of movable vanes arranged so as to be positioned in a common plane that closes the inside of the annular flange. Further, the plurality of movable blades are attached radially, and each movable blade is provided so as to be rotatable about its axis and tiltable so as to deviate from the common plane.

The throttle valve further includes a plurality of rotating shims having an outer toric surface that matches the curvature of the inner circumferential surface of the annular flange and rotational support means providing a connection to the inner circumferential surface of the annular flange. Each shim is connected at its side to the movable vane in order to transmit rotation of the shim to the movable vane. Each shim further includes rim means for transmitting rotational movement of the edge of the shim to the edge of an adjacent shim.

The plurality of shims are arranged endlessly along the inner circumferential surface of the annular flange so as to be in a relationship that allows motion to be transmitted between the edges.

The throttle valve further includes a connecting means that is provided to pass from the outer circumferential surface to the inner circumferential surface of the flange and that transmits rotational motion from the outside of the flange to one of the plurality of shims. .

In the fully closed state of the valve, the plurality of radially arranged movable vanes lie in a common plane and close the inside of the annular flange. Each vane has a shim installed on the inner circumference of the annular flange. When the plurality of movable vanes are located in a common plane so as to close the inside of the annular flange, the outer annular surface of each shim fits the inner circumferential surface of the annular flange. In this way, when the valve is in the fully closed state, there is no gap between the plurality of movable vanes and the inner peripheral surface of the annular flange, and the passage of gas is completely blocked.

On the other hand, when attempting to open the valve, rotational motion may be applied from the outside of the flange via the connecting means. This rotational motion is transmitted to a shim, and as the shim rotates, the shims move along the inner circumferential surface of the annular flange in an edge-to-edge relationship that allows motion transmission. arranged endlessly. Therefore, if this shim rotates via the coupling means, all shims will rotate. When the shim rotates, the movable vane also rotates, opening the valve. Thus, the means for rotating the vanes are shims and coupling means, which are not located in the gas flow path, but are installed in the annular flange. In this way, when the valve is fully open, the mechanism for rotating the blades does not become an obstacle to the flow of gas. In other words, when the valve is fully open, the presence of any member that blocks the flow of gas can be minimized.

An advantage of this invention is that it provides greater efficiency in cryogenic pumps. This is due to the fact that the valve structure allows the pump port to be fully opened, allowing more gas to move through the pump port.

DESCRIPTION OF THE EMBODIMENTS The invention preferably comprises a cryogenic pump having two stages, one of which is arranged coaxially with the hub, and a throttle valve combination. Before explaining the entire cryogenic pumping system, we will first explain the structure of the throttle valve.

a. Structure of Throttle Valve FIG. 1 shows a throttle valve according to the present invention.

The valve is housed in an annular flange 11 having an upper surface 13 and an opposite lower surface, not shown. A plurality of holes 15 extend through opposing sides of the flange, which
This does not impair the gas barrier relationship between the outer circumferential surface 17 and the inner circumferential surface 19 of the annular flange 11.

Between the upper surface 13 and the opposite lower surface, a large number of rotatable rotary shims 21, 22, 23, 24, etc.
They are installed circumferentially along the inner peripheral surface of the flange 11. These shims are connected to vanes 31, 32, 33, 34, etc. on their sides. Each shim occupies a space between each vane and the inner peripheral surface 19 of the flange. Each shim is rotatably attached to the inner circumferential surface 19 of the flange like a bearing, that is, rotatably. Since each shim and each blade are connected, when each shim rotates, the blade also moves accordingly.

Each blade is flat, plate-like, and wedge-shaped. This wedge-shaped blade has tips 41, 42, etc. at its tip (wedge tip). The tips 41, 42 of each blade are rotatably held by a hub 45, as shown in FIG. The wedge-shaped vanes are connected at their bases (wedge bases) to the sides of each shim.

All the shims arranged endlessly along the inner circumferential surface 19 of the annular flange 11 are mechanically connected to move in conjunction with each other. This will be discussed later. One shim or drive shim is rotationally driven by rotational energy applied from outside the annular flange 11. The remaining shims, the driven shims, are rotated by the rotational energy transferred from the drive shim.

As shown in FIG. 1, a bracket 47 is attached to the outer peripheral surface 17 of the annular flange 11 by screws 49. As shown in FIG. Bracket 47 holds actuator 51. This actuator 51 includes ports 55 and 57 that serve as fluid inlets and outlets, and a plunger that is moved by the fluid introduced into these ports. A servo control device, not shown, supplies fluid to ports 55 or 57;
The movement of plunger 53 is thereby controlled.
By controlling the movement of the plunger 53, opening and closing of the valve can be controlled.

Plunger 53, by its movement, displaces shaft 59, which is held in a sealed bearing.
Rotate. That is, a crank 61 is attached to the shaft 59, and this crank 61
The tip of the plunger 53 is connected to the tip of the plunger 53. Therefore, when the plunger 53 moves, the shaft 59 performs a rotational movement. Actuator 5
1, a manual stub 63 can also be used. adjusting the sleeve 67 using a manual or electric micrometer barrel 65;
The end of the movement of the crank 61 is defined. The micrometer barrel 65 can also be used to measure the position of the crank during various valve positioning operations.

Referring to FIG. 2, shims 25, 26 and 3
7 is adapted to close the space between the vanes 35, 36, 37 and the inner peripheral surface 19 of the flange. The portion of the shim facing the inner peripheral surface 19 of the flange is a toric surface. A toric surface is usually defined as a portion of the surface of a torus (doughnut-shaped). Typically, a torus includes a dominant radius for the entire torus and a minor radius, which is the cross-sectional radius. Here, the surface of the shim is given a toric surface due to the fact that it has a dominant radius corresponding to the radius of the inner peripheral surface of the flange. The arc defined by this radius lies in the same plane as the vane supported by the shim. According to this method, the arcs of adjacent shims are aligned when all the vanes are in the closed position, ie, when all the vanes are in a common plane that closes the inside of the annular flange. The edge-to-edge contact of the shims thus seals the opening in the inner peripheral surface 19 of the flange. To do this, it is only necessary that the shim have an arc in the plane of the vane that engages the inner peripheral surface of the flange. The remainder of the shim can have other curvatures. By having other curvatures, this shim can resemble the surface of an eyeglass lens, which is often toric.
This surface is called a torus.

As shown in FIG. 2, the shaft 59 is provided so as to pass from the outer peripheral surface 17 to the inner peripheral surface of the annular flange 11. As shown in FIG. This shaft 59 is
It acts as a coupling means for transmitting rotational motion from the outside of the flange 11 to one shim 26.
The shaft 59 is part of a sealed bearing, which is equipped with a commercially available type of shaft seal 69, such as a high-hydraulic seal or a conventional O-ring shaft seal.
Contains.

Referring to FIG. 3, a plurality of shims 26, 25,
An edge-to-edge arrangement of 28, 29, 30, 40 and 50 is evident. These shims are positioned such that the vanes connected to the shims form a common plane 38. The valve is therefore in the closed position. The inner peripheral surface 19 of the flange 11 is located away from the outer peripheral surface 17. The inner circumferential surface 19 and the outer circumferential surface 17 of the flange are connected to each other via a side wall in such a manner as to block gas flow therebetween. Inner peripheral surface 1 of flange 11
9 is located between a plane containing the upper surface 13 and a plane containing the lower surface 14 of the side wall. The common plane 38 is located parallel to the upper surface 13 and lower surface 14 of the side walls. The upper surface 13 and lower surface 14 of the sidewalls both have lip regions 16 and 18 that form an overhanging region. These lip areas 16 and 1
8 serves to hide the shim from the gas flow path, ie the path between the pump and the processing chamber. Thus, when the valve is fully open, it provides a very low impedance path for gas flow, with the exception of hub 45. There is no impeller flow blockage as in conventional devices.

The hub 45 is assembled from two discs 46 and 48 connected to each other by screws 52. The two disks have slots for receiving annular pins 71, 73 connected to the vanes. It is important that the hub is constructed from two discs in order to be able to install the vane and shim assembly before installing the hub. Only after everything is installed, vanes and shims, is the hub in place.

FIG. 4 shows a shim 21 having an outer toric surface having an arcuate surface area that conforms to the arm curve of the inner circumferential surface 19 of the flange 11. As shown in FIG. The opposite side of shim 21 is connected to vane 31 . Feather 31
is wedge-shaped and has a wedge tip 71 at its tip (wedge tip). This wedge tip becomes a pivot pin that fits into a corresponding opening formed in the hub. The opposite side of the vane 31 is a wedge base 72, which is connected to the shim along a line that is in the same plane as the arcuate region of the toric surface of the shim that conforms to the arm curve of the inner peripheral surface of the flange. has been done. The toric surface 82 has a pin 74 extending therefrom and fitted into a shallow hole in the inner peripheral surface of the flange.
have.

Referring to FIG. 5, shim 21 has a circular outline. The pin 74 is located at the center of this circle, and the blade 31 passes through the center of the circle.

As shown in FIGS. 4 and 5, the shim 21
has a groove 76 in its edge. This groove is
It is used to pass cables that transmit edge-to-edge motion between multiple shims. In this embodiment, the groove 76 and the cable function as a rim means for transmitting the rotational movement of the shim edge to the adjacent shim edge. Another example of functioning as a rim means is to form teeth on the edges of the shim, the teeth interlocking with each other.

The circular form of the shim means that the torus of the shim is a truncated hemisphere. This is a preferred shape because of its ease of assembly.
Each shim has a guide pin 78. The guide pin 78 is fitted into a circumferential groove, ie, a guide slot, formed in the inner peripheral surface 19 of the flange 31. Such a circumferential groove is formed with a width equal to, for example, 20% of the distance between the top and bottom surfaces of the flange. However, the ratio is not limited to this.

Referring to Figure 3, the circumferential groove (guide slot) designated by reference numeral 84 ranges from 0° when all shims are in the same plane to approximately 90° when the valve is fully open. The purpose of this is to limit the amount of rotation of the shim during this period. In other words, the circumferential groove 84 prevents each blade from tilting at an angle of 90° or more.

Referring to FIG. 6, guide pin 78 projects in the same direction as pivot pin 74. The pivot pin 74 and the guide pin 78 function as rotational support means for rotatably supporting the shim on the inner peripheral surface of the annular flange.

FIG. 7 illustrates how rotational motion is transmitted between a plurality of shims. In this diagram, shims 28, 2
5, 26 and 27 are arranged adjacent to each other. Cable 86 winds around a groove 76 formed in the edge of the shim. The end of this cable is clamped by a retainer 88 connected to the flat part of the shim and secured by a screw 90. The serpentine configuration of cable 86 causes adjacent shims to rotate in opposite directions, as shown by arrows A and B.

FIG. 8 shows the blades 31, 32, 33, etc. rotating slightly due to the movement of the crank 61. In this position, the valve will be slightly open, allowing gas to flow through this opening. The micrometer barrel can be advanced to measure the position of the crank, or left in place to act as a stop at a desired location.

Only one shaft 59 passes through the annular flange 11. By doing so, the chance of gas leakage is minimized. This advantage makes the illustrated valve extremely important for vacuum system applications. However, it goes without saying that this valve can also be advantageously used in non-vacuum situations where it is necessary to regulate the flow of gas.

FIG. 9 shows another embodiment of the invention. In this embodiment, all but one blade are driven by the rotational energy applied to the drive shim 103 via the shaft 101.
It's starting to move.

All shims operate in a similar manner to the previous embodiments, except that shim 105 has a shaft 107 extending therethrough. Shaft 107 rotates independently of shim 105. Shaft 107 extends through annular flange 111 sealed by shaft seal 113. The vane 117 has another shaft seal 115 within the shim 105 that supports the shaft 107. Therefore,
Vane 117 can rotate independently of shim 105. Shaft 107 is directly connected to vane 117. This can be done, for example, by shaft 107
This is done by providing a slit at the end of the blade 117 and attaching a chip to the end of the blade 117 that fits into the slit.

From Figure 9, a total of 12 blades can be observed.
If all the blades are moved by the driving shim 103, the driving shim 103 will control the remaining 11 other driven shims, so no matter which blade moves, the movement of the 12 blades will be the same. I become confused. However, in the embodiment shown in FIG. 9, drive shim 103 controls only 11 blades. The remaining blade 117 is attached to the shaft 107.
independently controlled by

The shaft 101 that controls the drive shim 103 is
It is activated during initial pumping or when precise control is not required. That is,
Shaft 1 constituting the first seal shaft means
01 moves all the blades except for one blade when coarsely adjusting one valve. Once the desired pressure is achieved, the positions of all the vanes except vane 117 are fixed, after which vane 117 is moved independently by shaft 107, which constitutes the second seal shaft means. This allows precise valve adjustment.

The servo control device is connected to the shafts 101 and 10.
A signal can be provided to an actuator or motor that controls 7. Such servo control devices are well known. A servo control device capable of performing coarse and fine corrections independently may be used; alternatively, one control device may be used that operates only while the coarse correction is being made, and one controller that operates only while the coarse correction is being made; Two controllers may be used, with the other controller operating later or when only fine corrections are required. A closed loop servo system allows coarse corrections to determine when the desired pressure threshold is achieved. Below the desired pressure threshold only fine corrections are used.

Correction can be performed by two stepper motors, and a first stepper motor for coarse correction.
This can be done with an actuator of the type shown and a stepper motor for precise correction.

FIG. 10 is an operational diagram of the valve in FIG. 9;
Here, actuator 119 is used to control shaft 101, shim 103, and all other shims. In the state shown in FIG. 10, except for one blade 117, all of the remaining blades are
It is located in a common plane that closes the opening of the flange 111.

Each blade 117 is independently controlled by a shaft 107 driven by a motor 119. This vane 117, unlike the other vanes, is shown in an inclined position. In this position, gas can pass from one side of the flange to the other. 1st
Figure 0 illustrates fine control used in situations where coarse control is no longer effective. During fine control, motor 119 independently moves vane 117, which is the only vane that moves during fine correction.

The concepts of rough control and precise control are
The present invention is not limited to radial vanes and throttle valves, but can also be used in other types of vacuum throttle valves using vanes.

The control mechanism of the valve as shown in FIGS. 9 and 10 includes a group of N blades suitable for opening and closing the gas passage opening of the annular flange, and the N blades are controlled independently of each other. It can be thought of as consisting of two sets of blades. The first set is composed of (N-1) blades, which are mechanically connected and move together by the above-mentioned rotatable shim or the like. The first
The vanes of the group perform coupled movement by means of a first coupling means, such as a shaft 101 extending through the flange.

The second group of vanes, ie the Nth vane, is independently coupled to a second coupling means, such as shaft 107. A shaft 107 constituting the second connection means is supported within the flange and connects the first
N from the outside of the flange independently of the connecting means of
Transmits the opening and closing motion to the second blade.

As shown in FIGS. 9 and 10, shaft 107 passes through one shim 105 and rotates independently of this shim. In this method, (N-1)
The Nth vane provides coarse control while the Nth vane provides fine control. Both coarse and fine control modes are responsive to electrical signals from a controller that is in the loop of a closed loop servo.

b. Cryogenic Pump Structure FIG. 11 shows a cryogenic pump 131 having two stages. The first stage is the outer wall 1
33, the walls of which are cooled to an intermediate temperature of about 77°K. The term "outer wall" means that this wall is radially outward from the built-in 135. This inner wall 135 is accompanied by a second pumping stage kept at a low temperature, for example 14°K. The first and second pumping stages are coaxially arranged within a housing 137 exposed to ambient temperature. Thermal isolation between outer wall 133 and housing 137 is provided by appropriate spacing in vacuum.

The housing 137 has an upper annular rim 139 for connection to a vacuum component, valve or tube connecting the pump to the process chamber via an intermediate fitting. Very low pressure operation occurs within the processing chamber. Some of the intermediate fittings may include coarse pumps. This crude pump achieves an intermediate low pressure before the process chamber is exposed to the cryogenic pumping apparatus of the present invention.

The throttle valve disclosed herein reduces the amount of pumping performed by the cryogenic pump. A throttle valve may be used to gradually introduce the cryogenic pump into the line, or alternatively, the cryogenic pump may be used to maintain the desired pressure. In this case, it is also possible to maintain a uniform and low pressure by adjusting the degree of opening of the blades. When the vanes are fully opened, the full capacity of the pump can be utilized in the process chamber through the opening in the upper part of the pump.

In FIG. 11, vanes 141 and 143 are shown in the open position. These vanes are connected by a central hub 145 as previously described and by shims 151 and 153, respectively.
Supported by. These shims are attached to the outer wall 13
3 may be installed directly within the exterior wall 1.
33 may be mounted in an annular flange 155 that is press-fit into 33.

Shaft 157 projects through outer wall 133 and is made of an insulating material such as ceramic. This shaft 157 further uses a sealed bearing 159 to connect the housing 13.
It protrudes through 7. This shaft 157
As in the previous embodiment, only one vane, vane 143, is driven to provide a precise mode of operation.

Shim 151 connected to one blade 141
is moved by rod 161. This rod 161 projects through an opening 163 in housing 137 and a bellows 165. bellows 165
allows vertical movement of the rod 161 when the free end 167 of the rod moves vertically. Rod 161 provides a general mode of operation similar to the previously described embodiments.

The hub 145 is shown supporting a downwardly extending shield 169 which blocks radiation entering from the tip of the pump and prevents it from impinging on the second stage or inner wall 135.

One reason for installing shims in flanges that are to be inserted into external walls is that many cryogenic pumps are currently in use. Many of these pumps do not have adequate throttling systems. Typically, cryogenic pumps have a buttful system near their tip,
This prevents projectiles from impinging on the internal surfaces. The baffle may have its front or part removed to accommodate the vanes of the invention. Conventional baffles are fixed and do not provide any throttling effect. For these existing cryogenic pumps, the throttle valve does not fit, even though the opening located in the region of the tip of the outer wall is slightly smaller due to the presence of the flange 155 supporting the vanes. This increases the pumping efficiency of this valve when it is wide open. Typically, the outer wall itself may be machined to accommodate the seam in this machined area, although this increases cost.

Referring to FIG. 12, shim 151 supporting blade 141 is connected to rod 16 via pin 171
It is connected to the upper end of 1. When rod 161 is moved in the direction indicated by arrow A, shim 151 performs a rotational movement as indicated by arrow B, thereby causing vane 141 to move from a first position indicated by solid lines to a second position indicated by dashed lines 142. Rotate to position.

FIG. 13 shows another means for attaching a throttle valve to the opening of a cryogenic pump. The opening or upper region of the cryogenic pump has a lip 139 to which a flange 181 is connected. The flange 181 is connected to the outer annular member 18
3 and an inner annular member 185.
The inner and outer annular members are spaced apart in discrete relationship with each other. However, the inner annular member 185 is in thermal contact with the cooled outer wall 133.

In both FIGS. 11 and 13, the valve with vanes 141 and 143
The temperature is almost the same as 3. This vane therefore forms part of the first pumping stage. The inner annular member 185 is connected to the outer wall 133
It is attached to the top of the outer wall 133 by a lip 187 that extends slightly over the edge. Inner annular member 185 connects central hub 145 and shield 16
Support all wings, not just 9.

The vanes extend through the shaft 15 through both the inner and outer annular members 183 and 185.
7. This shaft 157 is
As mentioned before, it is a highly insulating material. The valve of this invention, as previously mentioned, requires rotation of shaft 157 or rod 1 for single mode operation.
61 and can be opened by any of the vertical movements of shaft 157 and rod 16 for coarse and fine modes of operation.
1 can also be opened separately.

Although the preferred shape of shield 169 is disc-shaped, other shapes may be used, such as conical or umbrella-shaped configurations. Comparing Figure 13 with Figure 11, we get
It will be seen that in FIG. 13 the throttle valve is added as an external unit to the cryo-pump, while in FIG. 11 the valve is located within the pump as a component.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a gas flow control valve according to the invention, with the vanes shown in the closed position. 2 is a partially cutaway plan view of the valve of FIG. 1; FIG. FIG. 3 is a cross-sectional view of the bulb of FIG. 1 taken along line 3--3. FIG. 4 is a side view of a shim and radial vane according to the invention. FIG. 5 is a cutaway front view of the shim and vane of FIG. 4 looking inward. FIG. 6 is a cross-sectional view of the shim of FIG. 5 along line 6--6. Figure 7 shows the line 7- in Figure 2.
7 shows the edge-to-edge arrangement and attachment of shims along the circumference; FIG. 8 is a perspective view of the gas flow control valve of FIG. 1 with the vanes in a partially open position; FIG. FIG. 9 is a partially cutaway plan view of another embodiment of the invention. FIG. 10 is a diagram showing the operation of this device similarly to FIG. 9. 11th
The figure is a side view of a cryogenic pumping device with a throttling valve installed therein. 12 is a side view taken along line 12-12 of FIG. 11. FIG. FIG. 13 is a cutaway side view of a cryo-pumping device with a throttling valve mounted on top of the cryo-pump opening. In the figure, 11, 111 and 181 are flanges, 21, 22, 23, 24, 25, 26, 2
7, 28, 29, 30, 40 and 50 are shims,
31, 32, 33, 34, 35, 36, 37, 3
8, 117, 141 and 143 are vanes, 45 and 145 are hubs, 59, 101, 107 and 157 are shafts, and 131 is a cryogenic pump.

Claims (1)

[Claims] 1. A cooled outer wall for a first stage pumping of a condensable gas at intermediate temperatures and a cooled inner wall for a second stage pumping of a condensable gas at a low temperature. a cryogenic pump having an opening facing the pumped processing chamber, further comprising a radial vane throttle valve disposed across the opening to throttle the opening; includes an annular flange having a continuous inner circumferential surface and a continuous outer circumferential surface spaced apart from the inner circumferential surface, and the inner circumferential surface and the outer circumferential surface are configured to allow gas to flow therebetween. The valve further includes a plurality of movable vanes positioned in a common plane closing the annular flange; The movable vanes are mounted radially, each movable vane being rotatable about its axis and tiltable so as to deviate from the common plane; a plurality of rotating shims having an outer annular surface adapted to the curvature of the surface and rotational support means providing a connection to the inner circumferential surface of the annular flange; the sides thereof are connected to each said movable vane for transmitting rotational motion to the edges of an adjacent shim; the plurality of shims are arranged endlessly along the inner circumferential surface of the annular flange so as to be in a relationship capable of transmitting motion between the edges, and the valve includes: The low-temperature pumping device further includes a connecting means that is supported by a portion of the flange from an outer circumferential surface to an inner circumferential surface and that transmits rotational movement from the outside of the flange to one of the plurality of shims. 2. The low temperature pumping device according to claim 1, wherein the plurality of blades are in thermal contact with the outer wall. 3. The cryogenic pumping device of claim 1, wherein the flange is located in the upper region of the opening.